Duchenne Muscular Dystrophy is a progressive and lethal X-linked myopathy caused by mutations and deletions in the Dystrophin gene located at Xp21. The treatment of DMD has been complicated by the need to induce dystrophin expression in a wide range of skeletal muscles and in the heart. Thus far, this has been impossible using cell-based therapies or chemical transfection approaches. Therefore, recent interest has focused on the use of viral-based somatic gene therapy approaches to program recombinant dystrophin expression in the skeletal and cardiac muscle of DMD patients. In the studies described in this application, we propose to use systemic delivery of replication-defective adenovirus vectors to program skeletal muscle- and cardiac-specific expression of a dystrophin mini gene in a large animal model of DMD. Adenovirus vectors were chosen for these studies because recent work from several groups including our own has demonstrated that they represent the only currently available viral delivery system that is capable of efficiently programming recombinant gene expression in a large percentage of non-replicating skeletal and cardiac muscle cells in vivo following systemic administration. Our proposed studies will make use of skeletal muscle- and cardiac-specific transcriptional regulatory elements previously cloned and characterized by our laboratory to restrict expression of the dystrophin gene to the appropriate muscle cell types. In order to circumvent technical difficulties associated with use of the 14 kb dystrophin cDNA, we will use a smaller, naturally-occurring deletion mutant of the dystrophin cDNA. The feasibility of treating DMD by the systemic administration of replication- defective adenoviruses will initially be assessed in xmd dogs, a canine model of muscular dystrophy that has been demonstrated by us to display genetic, histopathological and functional features that closely resemble those of the human disease. In the studies described in this proposal, we plan to (i) generate a series of recombinant, replication-defective adenoviruses containing either the firefly luciferase, bacterial lacZ, or human minidystrophin genes under the control of the cardiac and skeletal muscle-specific regulatory elements described above, (ii) optimize the method of administration of these vectors in neonatal dogs, (iii) administer dystrophin-expressing adenovirus vectors to xmd dogs, and (iv) assess the effects of this virus on disease progression and on skeletal and cardiac muscle function. In addition, we will carefully assess the safety and potential side effects of adenovirus administration in these animals. These studies will have direct relevance to the therapy of DMD. Additionally, they will have important implications for the treatment of a variety of other inherited myopathies.